window.requestAnimFrame = (function() {
	return window.requestAnimationFrame ||
		window.webkitRequestAnimationFrame ||
		window.mozRequestAnimationFrame ||
		function(callback) {
			window.setTimeout(callback, 500 / 60);
		};
})();

// now we will setup our basic variables for the demo/ /现在我们将设置为演示我们的基本变量
var canvas = document.getElementById('canvas'),
	ctx = canvas.getContext('2d'),
	// full screen dimensions/ /全屏幕尺寸
	cw = window.innerWidth,
	ch = window.innerHeight,
	// firework collection/ /烟花集合
	fireworks = [],
	// particle collection/ /粒子集合
	particles = [],
	// starting hue/ /开始色调
//	hue = 120,
	hue = 40,
	// when launching fireworks with a click, too many get launched at once without a limiter, one launch per 5 loop ticks
	//当发射烟花点击,立刻得到了太多没有限制器,一推出5循环蜱虫
	limiterTotal = 5,
	limiterTick = 0,
	// this will time the auto launches of fireworks, one launch per 80 loop ticks
	//这将自动发射的烟花,一个发射每80循环蜱虫
	timerTotal = 80,
	timerTick = 0,
	mousedown = false,
	// mouse x coordinate,鼠标x坐标
	mx,
	// mouse y coordinate鼠标y坐标
	my;

// set canvas dimensions //画布大小
canvas.width = cw;
canvas.height = ch;

// now we are going to setup our function placeholders for the entire demo
//现在我们要设置占位符整个演示功能

// get a random number within a range 范围内的随机数
function random(min, max) {
	return Math.random() * (max - min) + min;
}

// calculate the distance between two points计算两点之间的距离
function calculateDistance(p1x, p1y, p2x, p2y) {
	var xDistance = p1x - p2x,
		yDistance = p1y - p2y;
	return Math.sqrt(Math.pow(xDistance, 2) + Math.pow(yDistance, 2));
}

// create firework
function Firework(sx, sy, tx, ty) {
	// actual coordinates实际的坐标
	this.x = sx;
	this.y = sy;
	// starting coordinates
	this.sx = sx;
	this.sy = sy;
	// target coordinates目标坐标
	this.tx = tx;
	this.ty = ty;
	// distance from starting point to target从起点到目标的距离
	this.distanceToTarget = calculateDistance(sx, sy, tx, ty);
	this.distanceTraveled = 0;
	// track the past coordinates of each firework to create a trail effect, increase the coordinate count to create more prominent trails
	//追踪过去坐标的烟花来创建一个跟踪效果,增加协调数到创造更多杰出的轨迹
	this.coordinates = [];
	this.coordinateCount = 3;
	// populate initial coordinate collection with the current coordinates
	//填充初始坐标集合与当前坐标
	while (this.coordinateCount--) {
		this.coordinates.push([this.x, this.y]);
	}
	this.angle = Math.atan2(ty - sy, tx - sx);
	this.speed = 2;
	this.acceleration = 1.05;
	this.brightness = random(50, 70);
	// circle target indicator radius圆半径目标指标
	this.targetRadius = 5;
}

// update firework
Firework.prototype.update = function(index) {
	// remove last item in coordinates array//删除最后一个项目坐标数组
	this.coordinates.pop();
	// add current coordinates to the start of the array当前的坐标添加到数组的开始
	this.coordinates.unshift([this.x, this.y]);

	// cycle the circle target indicator radius循环圆半径目标指标
	if (this.targetRadius < 8) {
		this.targetRadius += 0.3;
	} else {
		this.targetRadius = 1;
	}

	// speed up the firework加快烟花
	this.speed *= this.acceleration;

	// get the current velocities based on angle and speed
	var vx = Math.cos(this.angle) * this.speed,
		vy = Math.sin(this.angle) * this.speed;
	// how far will the firework have traveled with velocities applied?
	this.distanceTraveled = calculateDistance(this.sx, this.sy, this.x + vx, this.y + vy);

	// if the distance traveled, including velocities, is greater than the initial distance to the target, then the target has been reached
	if (this.distanceTraveled >= this.distanceToTarget) {
		createParticles(this.tx, this.ty);
		// remove the firework, use the index passed into the update function to determine which to remove
		fireworks.splice(index, 1);
	} else {
		// target not reached, keep traveling
		this.x += vx;
		this.y += vy;
	}
}

// draw firework
Firework.prototype.draw = function() {
	ctx.beginPath();
	// move to the last tracked coordinate in the set, then draw a line to the current x and y
	ctx.moveTo(this.coordinates[this.coordinates.length - 1][0], this.coordinates[this.coordinates.length - 1][1]);
	ctx.lineTo(this.x, this.y);
	ctx.strokeStyle = 'hsl(' + hue + ', 100%, ' + this.brightness + '%)';
	ctx.stroke();

	ctx.beginPath();
	// draw the target for this firework with a pulsing circle
	ctx.arc(this.tx, this.ty, this.targetRadius, 0, Math.PI * 2);
	ctx.stroke();
}

// create particle
function Particle(x, y) {
	this.x = x;
	this.y = y;
	// track the past coordinates of each particle to create a trail effect, increase the coordinate count to create more prominent trails
	this.coordinates = [];
	this.coordinateCount = 5;
	while (this.coordinateCount--) {
		this.coordinates.push([this.x, this.y]);
	}
	// set a random angle in all possible directions, in radians在所有可能的方向,设置一个随机角弧度
	this.angle = random(0, Math.PI * 2);
	this.speed = random(1, 20);//粒子喷射范围
	// friction will slow the particle down摩擦会使粒子慢下来
	this.friction = 0.95;
	// gravity will be applied and pull the particle down重力将应用粒子拉下来
	this.gravity = 1;
	// set the hue to a random number +-20 of the overall hue variable将颜色设置为一个随机数+ -20整体色调的变量
	this.hue = random(hue - 20, hue + 20);
	this.brightness = random(50, 80);
	this.alpha = 1;
	// set how fast the particle fades out设置粒子的速度消失
	this.decay = random(0.015, 0.03);
}

// update particle
Particle.prototype.update = function(index) {
	// remove last item in coordinates array
	this.coordinates.pop();
	// add current coordinates to the start of the array
	this.coordinates.unshift([this.x, this.y]);
	// slow down the particle
	this.speed *= this.friction;
	// apply velocity
	this.x += Math.cos(this.angle) * this.speed;
	this.y += Math.sin(this.angle) * this.speed + this.gravity;
	// fade out the particle
	this.alpha -= this.decay;

	// remove the particle once the alpha is low enough, based on the passed in index
	if (this.alpha <= this.decay) {
		particles.splice(index, 1);
	}
}

// draw particle
Particle.prototype.draw = function() {
	ctx.beginPath();
	// move to the last tracked coordinates in the set, then draw a line to the current x and y
	ctx.moveTo(this.coordinates[this.coordinates.length - 1][0], this.coordinates[this.coordinates.length - 1][1]);
	ctx.lineTo(this.x, this.y);
	ctx.strokeStyle = 'hsla(' + this.hue + ', 100%, ' + this.brightness + '%, ' + this.alpha + ')';
	ctx.stroke();
}

// create particle group/explosion
function createParticles(x, y) {
	// increase the particle count for a bigger explosion, beware of the canvas performance hit with the increased particles though
	//增加更大的粒子数爆炸,谨防画布与增加粒子的性能影响
	var particleCount = 200;
	while (particleCount--) {
		particles.push(new Particle(x, y));
	}
}

// main demo loop
function loop() {
	// this function will run endlessly with requestAnimationFrame
	requestAnimFrame(loop);

	// increase the hue to get different colored fireworks over time
	//hue += 0.5;

	// normally, clearRect() would be used to clear the canvas
	// we want to create a trailing effect though
	// setting the composite operation to destination-out will allow us to clear the canvas at a specific opacity, rather than wiping it entirely
	ctx.globalCompositeOperation = 'destination-out';
	// decrease the alpha property to create more prominent trails
	ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
	ctx.fillRect(0, 0, cw, ch);
	// change the composite operation back to our main mode
	// lighter creates bright highlight points as the fireworks and particles overlap each other
	ctx.globalCompositeOperation = 'lighter';

	// loop over each firework, draw it, update it
	var i = fireworks.length;
	while (i--) {
		fireworks[i].draw();
		fireworks[i].update(i);
	}

	// loop over each particle, draw it, update it
	var i = particles.length;
	while (i--) {
		particles[i].draw();
		particles[i].update(i);
	}

	// launch fireworks automatically to random coordinates, when the mouse isn't down
	//发射烟火自动随机坐标,当鼠标不下来
	if (timerTick >= timerTotal) {
		if (!mousedown) {
			// start the firework at the bottom middle of the screen, then set the random target coordinates, the random y coordinates will be set within the range of the top half of the screen
			//蛋挞烟花在屏幕中间的底部,然后设置随机目标坐标,随机y坐标将范围内的屏幕的上半部分
			fireworks.push(new Firework(cw / 2, ch, random(0, cw), random(0, ch / 2)));
			timerTick = 0;
		}
	} else {
		timerTick++;
	}

	// limit the rate at which fireworks get launched when mouse is down
	//极限的速度烟花鼠标按下时得到启动
	if (limiterTick >= limiterTotal) {
		if (mousedown) {
			// start the firework at the bottom middle of the screen, then set the current mouse coordinates as the target
			//启动烟花在屏幕中间的底部,然后将鼠标当前坐标设置为目标
			fireworks.push(new Firework(cw / 2, ch, mx, my));
			limiterTick = 0;
		}
	} else {
		limiterTick++;
	}
}

// mouse event bindings
// update the mouse coordinates on mousemove
canvas.addEventListener('mousemove', function(e) {
	mx = e.pageX - canvas.offsetLeft;
	my = e.pageY - canvas.offsetTop;
});

// toggle mousedown state and prevent canvas from being selected
canvas.addEventListener('mousedown', function(e) {
	e.preventDefault();
	mousedown = true;
});

canvas.addEventListener('mouseup', function(e) {
	e.preventDefault();
	mousedown = false;
});

// once the window loads, we are ready for some fireworks!
window.onload = loop();
//document.getElementById("monkey").onclick = function() {
//	loop();
//}